The viscosity of oil-based drilling fluid (mud) is higher after it returns to the surface than when it was injected in the wellbore due to a high solid content. Drill cuttings are transported to the surface in the drilling fluid. If a drilling fluid is too viscous, it will be difficult to pump. During drilling, after reaching the surface, the cuttings can be separated from the drilling fluid and the drilling fluid can be recirculated and reused. A settling pit can be used to separate the cuttings from the drilling fluid. If the solid particles are too fine (e.g., less than 0.1 nm), they may remain in suspension in the drilling fluid. The presence of the solid particles cause increased drilling fluid viscosity and gel strengths.
It would be advantageous to have a thinner that can be added to oil-based drilling fluid to reduce the viscosity of the oil-based drilling fluid after it returns to the surface so that the fluid can be reused.